Lime has been used in the treatment of sewage sludge to remove pathogens, lime stabilization of waste water, pasteurization of sludge and purification of drinking water by adjusting the pH of the water. Examples of such processes involving the use of lime can be found in U.S. Pat. Nos. 5,013,458; 5,229,011; 5,346,616; 5,401,402; 5,405,536; 5,433,844; 5,554,279; 5,618,442; and 7,416,673, which contents are incorporated herein by reference.
Calcium oxide (CaO), is mixed with water (H20) to form calcium hydroxide (Ca(OH)2). The chemical reaction which occurs during such mixing gives off heat in the form of an exothermic reaction. When this reaction is done in the presence of excess water it is commonly referred to as lime slaking. This process is accomplished in a device known as a lime slaker. The resulting mixture of Ca(OH)2 and water is known as a lime slurry and is referred to as a hydrated lime or quicklime or Ca(OH)2 and has water trapped in it. There is no further exothermic reaction after the lime slaking occurs.
Lime slurries are known to have some unique properties, one of which is an inherent ability to form scale on surfaces which come into contact with the lime slurry. The formation of scale, or “scaling” can render the various delivery systems, such as pipes, troughs, conduits, etc. unusable over time due to the build-up of scale. Such scale build-up requires frequent cleaning and descaling of the equipment that is used to handle lime slurries. Cleaning and descaling operations can be considerably labor and cost intensive.
Lime slurries also contain a certain amount of inert material that is commonly referred to as grit. Grit results because the lime contains a certain amount of material other than calcium oxide (CaO). Typically, quicklime is more than 90% pure and contains approximately up to 8% inert material or grit.
The presence of grit in a lime slurry can cause numerous problems, including grit build-up in downstream process chambers or vessels, grit acting to plug or clog nozzles or any orifices through which the slurry passes, and abrasions caused to treatment equipment and slurry delivery equipment such as pumps, pipes, valves, etc. because of the abrasive nature of grit particles.